Burner, hydrogen generator, and fuel cell power generation system

ABSTRACT

A burner comprises a fuel distributor having a plurality of fuel injection holes through which a fuel gas is injected into a combustion space  3 , an air injector  2  placed to surround the fuel distributor and having a plurality of air injection holes through which air is injected into the combustion space  3 , a temperature detector placed such that a temperature detecting portion at a tip end thereof is located within the air injection hole, a body portion thereof is contained within the air injector, and an air layer is formed between the temperature detector and an inner wall of the air injector  9 , and a flame detector connected to the temperature detector, for detecting a flame condition based on temperature information within the combustion space which is obtained from the temperature detector.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a burner. Particularly, thepresent invention relates to a burner configured to perform combustionusing a fuel gas containing a high content of hydrogen and a low contentof hydrocarbon based substance. More particularly, the present inventionrelates to a burner used in a hydrogen generator configured to generatehydrogen to be supplied to apparatus using hydrogen such as a fuel cell,from a fuel gas mainly containing a hydrocarbon based substance as acompound containing at least carbon and hydrogen, for example, a naturalgas, LPG, gasoline, naphtha, coal oil, or methanol, or a burnerconfigured to combust a fuel gas containing hydrogen as a majorcomponent such as an off-gas delivered from the fuel cell, to generateheat to be used for air-conditioning or supplying hot water.

[0003] 2. Description of the Related Art

[0004] In a fuel cell power generation system, a hydrogen generator thatgenerates hydrogen to be supplied to a fuel cell is configured such thatwater is added to a fuel gas mainly containing a hydrocarbon basedsubstance, such as a natural gas, LPG, gasoline, naphtha, coal oil, ormethanol, and the resulting mixture is heated at 650 to 700° C., so thatthe fuel gas is reformed to allow hydrogen to be taken out (reformingreaction). The reformed gas containing a high content of hydrogenobtained by the reforming reaction is supplied to the fuel cell and usedfor power generation. Heating in the reforming reaction is performed byusing a burner. The burner is configured to combust the fuel gas and airto generate a flame, thereby generating heat. In the hydrogen generator,using the heat generated by the burner, the heating for the reformingreaction is performed. As a fuel gas of the burner, for example, anoff-gas delivered from the fuel cell is used for efficient use of a feedgas. The off-gas contains a high content of hydrogen because it containslarge amount of hydrogen which remains unused after the reaction in thefuel cell and hence has high reactivity. For this reason, when a mixtureof the off-gas as the fuel gas and the air is supplied to a combustionspace (or chamber), the problem that the flame flows back will arise. Insuch a situation, problems associated with safety arises. Accordingly,in the burner, the off-gas and the air are independently supplied to thecombustion space.

[0005] In the burner configured as described above, in order to detectignition mistake, vanishment of flame, abnormal combustion, or the likefor the purpose of safe and efficient combustion, a flame rod extendsfrom outside to an inside of the combustion space to detect the flame(see Japanese Laid-Open Paten Application Publication No. 2001-201046.An igniter installed in an upper space of the combustion space isadapted to perform ignition (see Japanese Laid-Open Patent ApplicationPublication No. Hei. 7-22043).

[0006] In a flame detecting method using the flame rod, a voltage isapplied between the flame rod in contact with the flame generated withinthe combustion space and a burner body, and a current generated by ionsresiding within the flame is detected, so that the flame is detectedbased on the current. The flame detecting method using the flame rod isadvantageous when numerous ions are generated during a combustionreaction generating the flame, for example, the fuel gas containinglarge amount of carbon hydrogen based combustible substances. However,when the fuel gas containing a high content of hydrogen and a lowcontent of the hydrocarbon based combustible substance is combusted asdescribed above, no ions are generated in a combustion reactiongenerating the flame. For this reason, no current flows when the voltageis applied between the flame rod and the burner body, and it istherefore difficult to detect the flame.

[0007] Meanwhile, in the hydrogen generator, a hydrogen-rich gasgenerated during start and containing H₂ as a major component containslarge amount of CO in addition to H₂. Such a hydrogen-rich gas(hereinafter referred to as a generated gas) is not supplied to the fuelcell because CO contained in the gas degrades an electrode of the fuelcell. Accordingly, the generated gas is also used as the fuel gas of theburner for efficient use as in the case of the off-gas. As describedabove, in the hydrogen generator, the hydrocarbon based substance (e.g.,CH₄) contained in the fuel gas is converted into H₂ and CO₂ by thereforming reaction. Therefore, the hydrocarbon based combustiblesubstance remaining unconverted, which is contained in the generatedgas, is less. For this reason, in the combustion reaction using thegenerated gas as the fuel gas, generated ions, are less as in the caseof using the off-gas. So, when the flame detecting method using theflame rod is applied, the current detected when applying the voltagebetween the flame rod and the burner body is small, and it is thereforedifficult to detect the flame as in the case of using the off-gas.

[0008] In the burner of the hydrogen generator in the fuel cell powergeneration system, a current value detected by the flame rod isconverted into a voltage value, and it is judged whether or not a flamehas vanished based on whether or not the voltage value is smaller than athreshold voltage for judgment of vanishment of the flame. When thevoltage value is lower than the threshold voltage, it is judged that theflame has vanished and an operation is stopped. It should be noted that,in the burner to which the off-gas or the generated gas is supplied asthe fuel gas, the current value detected by the flame rod is smallbecause of small amount of ions residing in the flame, and hence, thevoltage value is small. For this reason, if the threshold voltage usedfor judgment of vanishment of the flame is set relatively higher, thevoltage value obtained by detection becomes below the threshold voltage,and it is judged that the flame has vanished regardless of generation ofthe flame. In view of this, it is necessary to set the threshold lower.But, in such a case, there is a possibility that misjudgment is made dueto variation in the value caused by noises in a component of a system.As should be appreciated from the above, when combustion is performedusing the off-gas or the generated gas as the fuel gas, it is difficultto detect the flame with high accuracy in the flame detecting methodusing the flame rod.

[0009] In addition, in the above configuration of the burner, thereexists a need for a space in the vicinity of the combustion space inwhich the flame rod is provided or a discharge electrode for ignition isprovided. However, in the configuration provided with the aboveinstallation spaces, combustion heat from the burner is transmitted tothe space which should not be heated, and is radiated therefrom. Thisreduce efficiency of heat transmission to the hydrogen generator to beheated. Further, the installation space increases a size of the burner,and hence reduce a space around the burner. As a result, theconfiguration around the burner is difficult to design flexibly.

SUMMARY OF THE INVENTION

[0010] The present invention has bee made under the circumstances, andan object of the present invention is to provide a burner capable ofaccurately detecting a flame in combustion of a fuel gas containing alow content of hydrocarbon based combustible substance. Another objectof the present invention is to provide a burner capable of efficientlyheating an object to be heated while inhibiting heat radiation to anobject other than the object to be heated, and having a compactconfiguration with flexibility increased around the burner.

[0011] According to the present invention, there is provided a burnerhaving a fuel distributor configured to inject a fuel supplied from afuel supply device; and an air injector placed such that the airinjector surrounds the fuel distributor so as to form a combustion spacearound the fuel distributor and having an air injection hole throughwhich air supplied from an air supply device is injected, the airinjected from the air injection hole and the fuel injected from the fueldistributor being combusted to allow a flame to be generated in thecombustion space, the burner comprising a temperature detector fordetecting a temperature of the combustion space, the temperaturedetector having a temperature detecting portion located within the airinjection hole or in an air flow passage of the combustion space; and aflame detector for detecting a condition of the flame within thecombustion space, based on the temperature detected by the temperaturedetector.

[0012] In accordance with such a configuration, since the flamecondition is detected by detecting the temperature within the combustionspace using the temperature detector, the flame can be detectedaccurately and correctly regardless of the type of the fuel gas incombustion using a fuel gas containing a low content of hydrocarbonbased combustible substance.

[0013] The temperature detector may be placed such that the temperaturedetecting portion is located within the air injection hole or within thecombustion space in the vicinity of the air injection hole.

[0014] In accordance with such a configuration, since the temperaturedetecting portion is located within the air injection hole or within thecombustion space in the vicinity of the air injection hole, thetemperature detecting portion is not heated up to the temperature ashigh as that of the combustion space. Therefore, the temperaturedetector can detect the temperature within a heat-resistance limit, anddegradation of the temperature detector due to heat can be avoided. Inaddition, since the temperature detector is placed so as to protrudeslightly into the combustion space, detection of the temperature withinthe combustion space can be carried out without disturbing the flamegenerated within the combustion space. These effects are remarkable inthe configuration in which the temperature detector is placed such thatthe temperature detecting portion is located within the air injectionhole.

[0015] The temperature detector may be placed so as to penetrate the airinjector.

[0016] It is preferable that the temperature detecting portion of thetemperature detector is thermally insulated from an inner face of theair injection hole.

[0017] In accordance with such a configuration, since the temperaturedetecting portion of the temperature detector is placed to be thermallyinsulated from the air injection hole, temperature variation within thecombustion space can be detected smoothly without being affected by theair injector.

[0018] It is preferable that a gap is formed between the temperaturedetector and the inner face of the air injector, and a width of the gapis substantially uniform over an outer periphery of the temperaturedetector.

[0019] In accordance with such a configuration, the temperature detectoris thermally insulated from the air injection hole by the air layerexisting within the gap. In addition, since flow of air toward thecombustion space is formed within the air layer, the temperaturedetecting portion of the temperature detector can be cooled quickly bythe flow of the air when the flame has vanished. This follows thatvanishment of the flame can be detected immediately. In particular,since uniform flow of air is formed in the air layer in the structure inwhich the width of the air layer is substantially uniform over theentire outer periphery of the temperature detector, the air can besupplied stably and combustion state can be stabilized.

[0020] It is preferable that the air injector has a plurality of airinjection holes, and a cross-sectional area of the gap between the airinjection hole within which the temperature detector is provided and thetemperature detector is substantially equal to a cross-sectional area ofthe air injection hole within which the temperature detector is notprovided.

[0021] In accordance with such a configuration, disorder of an injectionstate of the air which is caused by provision of the temperaturedetector within the air injection hole, can be inhibited, and the aircan be injected through the air injection hole within which thetemperature detector is provided, as in other air injection holes.Thereby, the flame can be generated in proper balance and stably.

[0022] The temperature detector may have the temperature detectingportion at an end portion thereof, and a body of the temperaturedetector is contained within the air injector.

[0023] In accordance with such a configuration, the space in which thetemperature detector is installed is unnecessary. This makes it possibleto avoid heat radiation to such an installation space, and henceefficiently heat an object to be heated. Further, the burner can besmall-sized, and flexibility of the configuration around the burner canbe improved.

[0024] An end portion of the temperature detecting portion side of thetemperature detector may be substantially covered with an oxidationfilm.

[0025] When using the temperature detector whose end portion is notcovered with the oxidization film, the oxidization film is formed bycombustion, so that the temperature varies due to the oxidization film.On the other hand, by using the temperature detector whose one endportion is covered with the oxidization film, accuracy of detection canbe improved because variation in the detected temperature due toformation of the oxidization film does not occur.

[0026] An end portion of the temperature detecting portion side of thetemperature detector may be substantially hemispherical.

[0027] In accordance with such a configuration, the temperature detectorcan be cooled quickly by the smooth flow of the air along the outerperiphery of the tip end when combustion by the burner stops. Duringcombustion, the temperature detector is subjected to heat radiation,which makes it easy to detect a temperature increase. Therefore,accuracy of detection is improved.

[0028] The temperature detector may be a sheath-shaped thermo couple.

[0029] Thereby, the configuration of the present invention can be easilyachieved.

[0030] A plurality of temperature detectors may be provided at differentpositions within the combustion space to detect temperatures ofdifferent regions within the combustion space.

[0031] In accordance with such a configuration, since a plurality oftemperature detectors can detect temperatures in different regions ofthe combustion space, detection of the flame can be carried out morecorrectly and accurately. In particular, by comparing the flameconditions in the regions of the combustion space to each other,detection of the abnormal combustion can be carried out accurately andsmoothly. Therefore, combustion is stopped immediately under theabnormal combustion condition, and as a result, discharge of CO andabnormally-high temperature condition can be avoided.

[0032] The combustion space may have a cross-sectional area thatincreases toward a flame radiation direction.

[0033] In accordance with such a configuration, combustion is stablyperformed in each region of the combustion space according to acombustion amount in a wide range.

[0034] The burner may further comprise an electrode contained within thefuel distributor and having an end portion that protrudes into thecombustion space; and an ignition circuit electrically connected to theelectrode, for applying a voltage to the electrode to allow electricdischarge from the electrode to occur within the combustion space.

[0035] In accordance with such a configuration, by applying a voltage tothe electrode to allow electric discharge to occur between the fueldistributor or the air injector and the electrode, ignition can takeplace. Since the electrode is contained within the fuel distributor, aspace for installing the ignition means becomes unnecessary. Because ofthe absence of such an installation space, heat radiation to the spacecan be avoided, and the object to be heated can be heated efficiently.In addition, the burner can be small-sized and flexibility of theconfiguration around the burner can be improved.

[0036] The burner may further comprise a switch configured to performswitching so that the electrode is connected to the ignition circuitduring ignition, and the electrode is connected to the flame detectorwhen the flame detector judges that ignition has occurred based ontemperature information of the combustion space from the temperaturedetector, wherein the flame detector detects the flame based on thetemperature information from the temperature detector and detects theflame based on an output current from the electrode.

[0037] In accordance with such a configuration, concurrently with theflame detection using the temperature detector, the conventional flamedetection using the electrode can be carried out. Therefore, the flamecan be detected more accurately and correctly. Such a configuration iseasily achieved without significant change, because the electrode as theignition means can be used to detect the flame,

[0038] The end portion of the electrode that protrudes into thecombustion space may be placed in a region different from a region ofthe combustion space in which the temperature detector is placed, todetect the flame in the region different from the region where the flameis detected by the temperature detector.

[0039] In accordance with such a configuration, the temperatures ofdifferent regions in the combustion space can be detected more correctlyand accurately by using the temperature detector and the electrode. Inparticular, by comparing the flame conditions in the regions of thecombustion space to each other, detection of the abnormal combustion canbe carried out easily, accurately and smoothly. Therefore, combustion isstopped under abnormal combustion condition, and as a result, dischargeof CO and abnormally-high temperature condition can be avoided.

[0040] The temperature detector may detect the flame in an upper regionof the combustion space in the flame radiation direction, and theelectrode may detect the flame in a lower region of the combustion spacein the flame radiation direction.

[0041] In accordance with such a configuration, the flame can bedetected in both of the upper and lower regions of the combustion space,a state in which ignition is detected in the upper region but ignitionis not detected in the lower region, and ignition is not detected in theupper region but ignition is detected in the lower region, can bedetected as the abnormal combustion condition.

[0042] According to the present invention, there is provided a hydrogengenerator comprising a burner having the above configuration, and areformer for generating a reformed gas containing hydrogen by areforming reaction of a hydrocarbon based material, wherein the burneris configured to heat the reformer.

[0043] In accordance with such a configuration, since the burner havingthe configuration is used, the flame can be detected accurately andcorrectly even when the gas containing a low content of hydrocarbonbased combustible substance is used as the fuel gas for the burner. Thehydrogen generator having such a configuration can generate the flamestably regardless of the type of the fuel gas while detecting the flame.

[0044] According to the present invention, there is provided a fuel cellpower generation system comprising the hydrogen generator having theabove configuration, and a fuel cell configured to generate a power,using a gas containing hydrogen as a major component which is suppliedfrom the hydrogen generator to a fuel electrode and an oxidizing gassupplied to an oxidizing electrode.

[0045] In accordance with the above configuration, since theabove-described effects are obtained in the hydrogen generator, theoff-gas or the generated gas containing hydrogen as a major component,is combusted as the fuel gas by the burner to generate heat for thereforming reaction. Consequently, it is possible to achieve a system inwhich power generation efficiency is high and burden on environment isless.

[0046] The above and further objects and features of the invention willmore fully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is a cross-sectional view schematically showing aconfiguration of a burner according to a first embodiment of the presentinvention;

[0048]FIG. 2 is a partially enlarged cross-sectional view schematicallyshowing placement of a temperature detector in FIG. 1;

[0049]FIG. 3 is a partially enlarged plan view schematically showingplacement of the temperature detector in FIG. 2;

[0050]FIG. 4 is a cross-sectional view schematically showing aconfiguration of a burner according to an alternative example of thefirst embodiment;

[0051]FIG. 5 is a cross-sectional view schematically showing aconfiguration of a burner according to a second embodiment of thepresent invention;

[0052]FIG. 6 is a cross-sectional view schematically showing aconfiguration of a burner according to a third embodiment of the presentinvention;

[0053]FIG. 7 is a cross-sectional view schematically showing aconfiguration of a burner according to a fourth embodiment of thepresent invention;

[0054]FIG. 8 is a view schematically showing a configuration of a fuelcell power generation system according to a fifth embodiment of thepresent invention; and

[0055]FIG. 9 is a view showing operation data of a hydrogen generator inthe fuel cell power generation system according to the fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Hereinafter, preferred embodiments of the present invention willbe described with reference to the accompanying drawings.

[0057] (Embodiment 1)

[0058]FIG. 1 is a cross-sectional view schematically showing aconfiguration of a burner according to a first embodiment of the presentinvention. FIG. 2 is a partially enlarged cross-sectional viewschematically showing placement of a temperature detector in FIG. 1, andFIG. 3 is a partially enlarged plan view schematically showing placementof the temperature detector in FIG. 2.

[0059] As shown in FIG. 1, the burner comprises a fuel distributor 1provided with a plurality of fuel injection holes 8, an air injector 2provided with a plurality of air injection holes 9, and a temperaturedetector 6 contained and placed within the air injector 2. A spacesurrounded by an inner peripheral wall 2B of the air injector 2 is acombustion space (or combustion chamber) 3. The temperature detector 6detects temperature of the combustion space 3.

[0060] The air injector 2 is cylindrical and are configured to open atboth ends. The air injector 2 is hollow and its internal shape is suchthat the inner peripheral wall 2B is inclined, thereby forming aninverted-frustum-cone shaped space in which a cross-sectional area of aninner hole of a cylinder increases toward an opening at the upper end(exit from which the flame radiates). In other words, the innerperipheral wall 2B forms a cup shape. The cup-shaped space correspondingto the inner hole of the air injector 2 forms the combustion space 3 inwhich the flame is generated and combustion is performed. The airinjector 2 has a hollow cylindrical peripheral wall portion. Theperipheral wall portion is configured such that an inner space 20 isformed by an outer peripheral wall 2A, the inner peripheral wall 2B, anupper end wall 2C, and a lower end wall 2D, and surrounds the combustionspace 3 in the circumferential direction. The inner space 20 of the airinjector 2 communicates with the combustion space 3 through theplurality of air injection holes 9 arranged both in the circumferentialdirection and in a vertical direction of the air injector 2. The innerspace 20 has an air supply port 31 provided in the outer peripheral wall2A, and an air supply device 5 provided outside is connected to the airsupply port 31. The air supply device 5 has an air blower (not shown)such as a pump or a fan, and is configured to supply air for combustionto the air injector 2 while adjusting its flow rate. The flow rate ofair supply is adjusted by controlling an operation of the air blower, orby controlling a flow rate adjuster provided downstream of the airblower such as a valve in a supply system.

[0061] The air injector 2 is, for example, made of metal. The airinjector 2 has a heat capacity larger than that of a temperaturedetector 6 mentioned later, because of its large volume. As shown inFIG. 2, the air injection holes 9 (9A and 9B) that are circular and havepredetermined diameters are formed in the inner peripheral wall 2Bforming the combustion space 3 at predetermined intervals. Here, the airinjection holes 9 are comprised of one air injection hole 9A having adiameter D1 of 2.0 mm and a number of air injection holes 9B having adiameter D2 of 1.2 mm. And, the temperature detector 6 is providedwithin the air injection hole 9A. The temperature detector 6 isconfigured such that a temperature detecting portion (not shown)provided at a tip end thereof slightly protrudes into the combustionspace 3 to face the combustion space 3 and to be located in flow of theair. And, a body of the temperature detector 6 extends through the innerspace 20 of the air injector 2 and through a penetrating hole 32 formedin a lower end wall 2D and its base end protrudes outside. Thetemperature detector 6 is supported by a support member (not shown), andsealing is created by a seal member (not shown) between the penetratinghole 32 of the air injector 2 and the temperature detector 6 in order toinhibit leakage of air. Here, as the temperature detector 6, asheath-shaped thermocouple having a diameter of 1.6 mm is used. The tipend portion including the temperature detecting portion (not shown) iscovered with an oxidization film 16. By covering the tip end portionwith the oxidization film 16, the temperature within the combustionspace 3 can be detected accurately as described later. The temperaturedetector 6 is placed so as not to be in contact with an inner face ofthe air injection hole 9A, and hence, there is a gap between thetemperature detector 6 and the inner face of the air injection hole 9A.As shown in FIG. 3, the temperature detector 6 is placed concentricallywithin the circular air injection hole 9A. Thereby, a width L of theannular air layer 17 formed on an outer periphery of the temperaturedetector 6 (i.e., distance between the inner peripheral face of the airinjection hole 9A and an outer peripheral face of the temperaturedetector 6) is substantially uniform over the entire outer periphery ofthe temperature detector 6. In the structure of the air injection hole9A within which the temperature detector 6 is placed, a cross-sectionalarea of a portion as an air flow passage (i.e., air layer 17) issubstantially equal to that of the air injection hole 9B, and the airflow passage having the uniform width L is formed on the outer peripheryof the temperature detector 6. Instead of the thermo couple, forexample, a thermistor or the like may be used as the temperaturedetector 6. The temperature detector 6 is connected to a flame detector7 provided outside of the burner.

[0062] The combustion space 3 has a cross-sectional area that decreasesfrom the upper portion (an exit from which the flame is radiated) towarda lower portion thereof. A fuel distributor 1 is fitted to the lowerportion of the combustion space 3. The fuel distributor 1 is pipe-shapedand its upper end is closed. The fuel distributor 1 is placed such thatan upper end portion provided with a plurality of fuel injection holes 8arranged in the circumferential direction protrudes into a centerportion of the combustion space 3 having a circular cross-section and alower end thereof is connected to the fuel gas supply device 4 providedoutside. The fuel gas supply device 4 is configured to supply the fuelgas containing a combustible gas to the fuel distributor 1 whileadjusting the flow rate of the fuel gas, and has the blower (not shown)such as the pump or the fan. The flow rate of the fuel gas is adjustedby controlling an operation of the air blower, or by controlling a flowrate adjustor provided downstream of the air blower such as the valve inthe supply system.

[0063] Subsequently, an operation of the burner during combustion willbe described.

[0064] As indicated by an arrow in FIG. 1, the fuel gas is supplied fromthe fuel gas supply device 4 to the fuel distributor 1. Further, thefuel gas is injected from the fuel distributor 1 into the combustionspace 3 through the fuel injection hole 8. As defined herein, the fuelgas supplied from the fuel gas supply device 4 refers to a combustiblegas containing hydrogen as a major component. As described later in anfifth embodiment (FIG. 8), as the fuel gas, a generated gas which isgenerated during start of the hydrogen generator in the fuel cell powergeneration system, or the off-gas of the fuel cell, may be used.

[0065] Meanwhile, air is supplied from the air supply device 5 to theair injector 2. As indicated by arrows in FIG. 1, the air is introducedinto the inner space 20 of the air injector 2, and is injected into thecombustion space 3 through the air injection holes 9. At this time, theflow rates of the air being injected from both of the holes 9A and 9Bare substantially equal, because the cross-sectional areas of the airflow passages of the air injection holes 9A and 9B are substantiallyequal. Therefore, disorder of an air injection state of the air due toplacement of the temperature detector 6 within the air injection hole 9Ais minimized, and disorder of a combustion state is inhibited. Inaddition, since the air flow passage having the uniform width L isformed on the outer periphery of the temperature detector 6 as describedabove, the air is injected substantially uniformly from the airinjection hole 9A in the outer peripheral region of the temperaturedetector 6. Therefore, disorder of the injection state of the air isfurther inhibited, and the disorder of the combustion state is furtherinhibited.

[0066] The fuel gas and the air which are thus supplied to thecombustion space 3 are mixed therein. And, ignition is performed usingan ignition device (not shown) such as gathering coal or a heater. Thefuel gas and the air are reacted to be combusted in the combustion space3, thereby generating a flame 10. As described above, since the air issupplied from the air injection holes 9A and 9B at substantially equalflow rate, the flame 10 can be generated stably and in proper balance.And, as indicated by an arrow, heat emitted from the generated flame istransmitted to an object to be heated. Thus, by supplying the fuel gasand the air independently to be combusted within the combustion space 3,combustion is carried out stably without back flow of the flame in thesupply system, which occurs in the conventional configuration in whichthe mixture of the combustible fuel gas and the air is supplied to andcombusted in the combustion space 3.

[0067] During the combustion, the condition of the flame is detectedusing the temperature detector 6 to know whether or not ignition, flamevanishment, or abnormal combustion has occurred. Hereinbelow, how theflame is detected will be described.

[0068] Upon the flame 10 being generated within the combustion space 3,the temperature within the combustion space 3 which had normaltemperature, increases, and hence, the temperature detector 6 detectsthe increased temperature. At this time, the temperature detector 6 isnot directly exposed to the flame of the combustion space 3, because thetemperature detecting portion (not shown) at the tip end thereof islocated within the air injection hole 9A of the air injector 2, and thebody thereof is contained within the inner space 20 of the air injector2. For this treason, during combustion, the temperature of thetemperature detector 6 does not increase to a high temperature (about1000° C.) up to which the temperature of the combustion space 3increases. Under this condition, the temperature detector 6 is placedunder the temperature within a heat-resistant limit, and degradationthereof is avoided. In addition, since the temperature detector 6protrudes only slightly into the combustion space 3, the temperaturewithin the combustion space 3 can be detected without disturbing theflame generated within the combustion space 3.

[0069] In addition, since the temperature detecting portion (not shown)at the tip end of the temperature detector 6 faces the combustion space3, the temperature within the combustion space 3 can be detectedaccurately and smoothly. It should be noted that the tip end at whichthe temperature detecting portion is provided is not directly in contactwith the inner face of the air injection hole 9A, and is therebythermally insulated from the air injector 2 because of the presence ofthe air layer 17 formed around the temperature detector 6. Accordingly,the temperature detector 6 can detect variation in the temperaturewithin the combustion space 3 without being affected by the variation inthe temperature of the inner peripheral wall 2B of the air injector 2.In other words, since the temperature of the temperature detectingportion of the temperature detector 6 increases more quickly than thetemperature of the inner peripheral wall 2B of the air injector 2 havinga large heat capacity increases, the ignition can be detected smoothly,accurately, and correctly.

[0070] Temperature information of the combustion space 3 detected by thetemperature detector 6 is transmitted to the flame detector 7 in theform of an electric signal. Upon reception of the electric signal, theflame detector 7 judges whether or not the flame 10 has been generatedwithin the combustion space 3 (i.e., ignition has occurred) based on thetemperature variation in the combustion space 3. To judge whether or notthe ignition has occurred, it may be judged whether or not the detectedtemperature of the combustion space 3 is higher than a predeterminedtemperature, or otherwise, it may be judged whether or not temperatureincreasing rate per unit time is higher than a predetermined temperatureincreasing rate.

[0071] If the flame has vanished for some reasons, then the temperatureof the combustion space 3 which was kept high is rapidly reduced.Correspondingly, the temperature detected by the temperature detector 6is reduced. The reduced temperature information of the combustion space3 is transmitted to the flame detector 7 in the same manner as describedabove. Upon reception of the electric signal, the flame detector 7judges whether or not the flame 10 has vanished within the combustionspace 3 based on the temperature variation. To judge whether or not theflame 10 has vanished, it may be judged whether or not the detectedtemperature of the combustion space 3 is lower than a predeterminedtemperature, or otherwise, it may be judged whether or not temperaturereducing rate per unit time is higher than a predetermined temperaturereducing rate. As described above, since the air layer 17 is formed inthe gap between the temperature detecting portion of the temperaturedetector 6 and the inner face of the air injection hole 9A, thetemperature of the temperature detector 6 is reduced quickly soon afterthe flame 10 has vanished without being affected by the air injector 2.Especially, in the air layer 17 formed between the temperature detector6 and the inner face of the air injection hole 9A, the air flows towardthe combustion space 3 by supply of the air, and the temperaturedetector 6 is located in the flow of air. By the flow of the air, thetemperature detector 6 is cooled quickly, and the temperature of thetemperature detecting portion of the temperature detector 6 is reducedrapidly when heating stops after the flame 10 has vanished. Therefore,it is possible to detect vanishment of the flame 10 in a short timeafter the flame 10 has vanished.

[0072] In accordance with the flame detecting method described above,since the flame 10 can be detected based on the temperature variationwithin the combustion space 3 regardless of a current value duringcombustion unlike in the conventional method. As a result, even in thecombustion using the fuel gas that is difficult to detect by theconventional detecting method using the flame rod, or the like, i.e.,the fuel gas containing a low content of hydrocarbon based combustiblesubstance, the flame condition can be detected accurately and correctly.

[0073] As described above, since the tip end on the temperaturedetecting portion (not shown) side of the temperature detector 6 iscovered with the oxidation film 16, the temperature within thecombustion space 3 can be detected more accurately as compared to thedetecting method using the temperature detector without the oxidationfilm. The reason for this will be described below. In the case where thetemperature detector which is not covered with the oxidation film isused, the tip end of the temperature detector is oxidized by thecombustion within the combustion space 3, and in time, the oxidationfilm is formed. In this case, the temperature detected by thetemperature detector 6 varies due to formation of the oxidization film.On the other hand, in the case where the oxidation film 16 is formed onthe tip end of the temperature detector 6 as described above, thevariation in the detected temperature can be avoided. Therefore, theflame can be detected more accurately.

[0074] Furthermore, in the above configuration, since the combustionspace 3 is cup-shaped, i.e., inverted-frustum-cone shaped to have thecross-section that increases toward the upper portion (flame radiationexit), the flame 10 can be generated stably and in proper balanceaccording to a combustion amount in a wide range. Specifically, in thecase where the flow rate of a mixture gas of the fuel gas and the air asa combustion source is small and hence the amount of combustion iscorrespondingly small, the flow rate and combustion speed of the mixturegas are balanced in a region of the combustion space 3 having asmall-cross-sectional area. The size of the flame is determined by thebalance between the flow rate and combustion speed (reaction rate of thecombustion reaction) of the mixture gas as the combustion source. Whenthe amount of combustion is thus small under the condition in which thecombustion speed is constant, a flame 10A is generated in substantiallythe lower region of the combustion space 3. On the other hand, when theflow rate of the mixture gas is high and hence the amount of combustionis correspondingly large, the mixture gas flow rate and the combustionspeed are balanced in a region of the combustion space 3 that has alarge cross-sectional area. Therefore, in this case, a flame 10B isgenerated in substantially the upper region of the combustion space 3.Thus, the cup-shaped combustion space 3 enables stable combustion in awide range of combustion amount. The air injector 2 having thecup-shaped combustion space 3 is easily constituted by one component bypress forming or drawing. Here, the flame is defined as ahighest-temperature portion at a boundary between the region wherecombustion is being performed and the region where combustion is notperformed. In other words, the flame is an outermost portion of thegenerated flame.

[0075] Further, since the temperature detector 6 is placed to becontained within the air injector 2, a space for installing thetemperature detector becomes unnecessary unlike the conventional methodusing the flame rod as the temperature detector. That is, aninstallation space need not be provided around the burner. Since heatradiation from the installation space is avoided, the object to beheated can be heated efficiently. The size of the burner can be reducedbecause of the absence of such an installation space. As a result, theflexibility of the configuration around the burner can be greatlyimproved.

[0076] The hole diameter of the air injection holes 9A and 9B, thediameter of the temperature detector 6, and the shapes of these are onlyillustrative and are not intended to be limited to those describedabove. In addition, the cross-sectional areas of the air injection holes9A and 9B are not necessarily equal, but may be different from eachother so long as the air layer 17 is formed around the temperaturedetector 6. Furthermore, the width L of the air layer 17 may benon-uniform. As an alternative example of this embodiment, thecombustion space 3 surrounded by the air injector 2 may be cylindricalto have a uniform cross-sectional area, instead of the cup-shape shownin FIG. 1.

[0077]FIG. 4 is a partially enlarged cross-sectional view schematicallyshowing a configuration of the burner according to the alternativeexample of the first embodiment. As shown in FIG. 4, the burner of thisalternative example is substantially identical in configuration to theburner in FIG. 1 except the following respects.

[0078] In the burner of this alternative example, the tip end of thetemperature detecting portion (not shown) side of the temperaturedetector 6 placed within the air injection hole 9A is hemispherical. Thetip end of such a shape is subjected to heat radiation more than the tipend having a corner portion, and therefore, allows the temperatureincrease caused by combustion to be detected accurately by thetemperature detector 6. The tip end of such a shape is easily cooled bysmooth air flow formed along a smooth surface of the hemisphericalshape, and upon vanishment of the flame, the temperature of the tip endis rapidly reduced. So, the vanishment of the flame can be detectedaccurately. As should be appreciated from the foregoing, in accordancewith the configuration of this alternative example, the above effectscan be produced more efficiently.

[0079] (Embodiment 2)

[0080]FIG. 5 is a cross-sectional view schematically showing aconfiguration of the burner according to a second embodiment of thepresent invention. The burner of this embodiment is substantiallyidentical in configuration to the burner of the first embodiment exceptthat a plurality of temperature detectors are placed at differentpositions in the combustion space.

[0081] In addition to the temperature detector 6 provided as describedin the first embodiment, in the second embodiment, a temperaturedetector 60 is provided so as to be located lower than the temperaturedetector 6. The temperature detector 60 is connected to the flamedetector 7 to allow temperature information relating to a lower regionof the combustion space 3 detected by the temperature detector 60 to betransmitted to the flame detector 7 in the form of an electric signal.As in the temperature detector 6, the temperature detector 60 isconfigured such that a tip end of the temperature detecting portion (notshown) side is covered with the oxidation film 16. Also, as in thetemperature detector 6, the temperature detecting portion (not shown) islocated within the air injection hole 9 to be in the air flow, and anair layer having a uniform width is formed on an outer periphery of thetemperature detector 60. Therefore, in accordance with the temperaturedetector 60, the temperature of the lower region of the combustion space3 can be detected accurately and correctly as in the temperaturedetector 6. In addition, as in the first embodiment, the temperature ofthe upper region of the combustion space 3 can be detected accuratelyand correctly by the temperature detector 6. Thus, temperatures ofdifferent regions of the combustion space 3, i.e., the upper region andthe lower region are respectively detected, and ignition states of theseregions are compared to another. Thereby, in particular, abnormalcombustion can be detected easily and correctly. When it is judged thatthe abnormal combustion has occurred, for example, supply of the fuelgas from the fuel gas supply device 4 is stopped to cause combustion tostop. Thus, discharge of CO due to abnormal combustion or degradation ofdevices including the burner due to elevated temperature, can beavoided. Hereinbelow, how the abnormal combustion is detected will bedescribed in detail.

[0082] First, in the case where combustion is performed normally, and aflame 11C is thereby generated, the temperature of the combustion space3 becomes substantially uniform. So, the temperature detected by thetemperature detector 6 provided in the upper region of the combustionspace 3 (in the vicinity of the exit of the combustion space 3) becomessubstantially equal to the temperature detected by the temperaturedetector 60 provided in the lower region of the combustion space (in thevicinity of the fuel distributor 1), and the flame detector 7 judgesthat ignition has occurred in both of the upper and lower regions of thecombustion space 3. So, in this case, it is confirmed that combustion isbeing performed normally within the combustion space 3.

[0083] However, for example, if the combustion amount becomes too large,or the amount of air supply is small for some reasons, thereby causingthe flame to be lifted to some degrees, abnormal combustion takes place,and a flame 11B is generated in substantially the upper region of thecombustion space 3. The flame 11B causes the upper region of thecombustion space 3 to be heated greatly, thereby resulting in atemperature of this upper region higher than normal. So, the temperaturedetected by the temperature detector 6 provided in the upper region ofthe combustion space 3 becomes high. Conversely, the temperaturedetected by the temperature detector 60 provided in the lower region ofthe combustion space 3 becomes low because of absence of the flame.Temperature information of the upper region of the combustion space 3which has been detected by the temperature detector 6 and temperatureinformation of the lower region of the combustion space 3 which has beendetected by the temperature detector 60 are respectively transmitted tothe flame detector 7, which judges flame conditions based on theseinformation. In this case, since it is detected that the temperature ofthe upper region of the combustion space 3 is higher than apredetermined value, based on the temperature information from thetemperature detector 6, the flame detector 7 judges that that ignitionhas occurred in the upper region of the combustion space 3. On the otherhand, since it is detected that the temperature of the lower region ofthe combustion space 3 is lower than the predetermined value, based onthe information from the temperature detector 60, the flame detector 7judges that the flame has vanished in the lower region of the combustionspace 3. As a result, it is confirmed that the flame 11B is abnormal.

[0084] If the combustion amount becomes too small, or the amount of airsupply becomes large for some reasons, abnormal combustion takes place,and a small flame 11A is generated in the lower region of the combustionspace 3. The flame 11A causes the lower region of the combustion space 3to be heated greatly, thereby resulting in a temperature of this lowerregion higher than normal. So, the temperature detected by thetemperature detector 60 provided in the lower region of the combustionspace 3 becomes high. Conversely, the temperature detected by thetemperature detector 6 provided in the upper region of the combustionspace 3 becomes low because of absence of the flame. Thus, based on thetemperature information of the upper region of the combustion space 3which has been detected by the temperature detector 6 and thetemperature information of the lower region of the combustion space 3which has been detected by the temperature detector 60, the flamedetector 7 judges the condition of the flame 11A within the combustionspace 3. In this case, since it is detected that the detectedtemperature of the upper region of the combustion space 3 is lower thana predetermined value, based on the temperature information from thetemperature detector 6, the flame detector 7 judges that the flame hasvanished in the upper region of the combustion space 3. On the otherhand, since it is detected that the detected temperature of the lowerregion of the combustion space 3 is higher than the predetermined value,based on the temperature information from the temperature detector 60,the flame detector 7 judges that ignition has occurred in the lowerregion of the combustion space 3. As a result, it is judged that theflame 11A is abnormal.

[0085] It should be noted that, the number of the temperature detectorsor placement of the same within the combustion space are not intended tothe above.

[0086] (Embodiment 3)

[0087]FIG. 6 is a cross-sectional view schematically showing aconfiguration of a burner according to a third embodiment of the presentinvention. The burner of this embodiment is substantially identical inconfiguration to the burner of the first embodiment except that anelectrode 12 as an ignition means is provided within the distributor 1.

[0088] More specifically, in this embodiment, the electrode 12 isprovided at the center of an inner hole of the fuel distributor 1 thatis pipe-shaped and has a double-walled structure. The electrode 12 issupported by a support member 15 fitted to the inner hole of the fueldistributor 1, and a tip end of the electrode 12 protrudes into thecombustion space 3. The support member 15 is made of ceramic or the likethat is heat-resistant and insulative. The protruding tip end portion ofthe electrode 12 is bent in an arc shape toward the inner peripheralwall 2B of the air injector 2. And, a base end of the electrode 12penetrates through a bottom wall of the fuel distributor 1 and protrudesto outside to be electrically connected to an ignition circuit 13provided outside. A seal member (not shown) is filled in a gap betweenthe electrode 12 and the support member 15 and in a gap between theinner peripheral wall of the fuel distributor 1 and the support member15.

[0089] In the above configuration, during ignition, the air is injectedfrom the air injection holes 9 of the air injector 2 into the combustionspace 3, and the fuel gas is injected from the fuel injection hole 8 ofthe fuel distributor 1 into the combustion space 3. Since the fueldistributor 1 has the double-walled structure, the electrode 12 and thesupport member 15 provided within the fuel distributor 1 do not inhibitthe fuel gas from being supplied from the fuel gas supply device 4 tothe distributor 1 and from being injected from the fuel injection hole8. Upon the fuel gas and the air being supplied into the combustionspace 3 and mixed therein, a voltage from the ignition circuit 13 isapplied to the electrode 12. This causes electric discharge between theelectrode 12 and the inner peripheral wall 2B of the air injector 2. Asa result, ignition takes place. Then, combustion is performed and theflame is generated within the combustion space 3. At this time, as inthe first embodiment, the temperature detector 6 detects the temperaturewithin the combustion space 3 and the flame detector, detects the flamecondition.

[0090] In accordance with the configuration of the second embodiment, inaddition to the effects provided by the configuration of the firstembodiment, effects described below is obtained. In the configuration ofthe second embodiment, since the electrode 12 functioning as theignition means is contained in the fuel distributor 1, the space forinstalling the ignition means around the burner, for example, above thecombustion space 3, becomes unnecessary unlike the conventionalconfiguration. Therefore, heat radiation from the installation space isavoided and the object to be heated can be heated efficiently. The sizeof the burner can be reduced because of the absence of the installationspace. As a result, flexibility of the configuration around the burnercan be further improved.

[0091] While ignition is performed in such a manner that electricdischarge is caused to occur between the electrode 12 and the innerperipheral wall 2B of the air injector 2, this may be performed byelectric discharge between the electrode 12 and the fuel distributor 1.In this case, to facilitate the electric discharge between the electrode12 and the fuel distributor 1, it is preferable that the tip end of theelectrode 12 that protrudes into the combustion space 3 is bent towardthe fuel distributor 1. It should be noted that the shape of theelectrode 12 is not intended to be limited to the above, that is, theelectrode is not necessarily bent.

[0092] (Embodiment 4)

[0093]FIG. 7 is a cross-sectional view schematically showing aconfiguration of a burner according to a fourth embodiment of thepresent invention. The burner of this embodiment is substantiallyidentical in configuration to the burner of the first embodiment exceptthat the ignition circuit 13 and the flame detector 7 are connected inparallel to the electrode 12 through a switch 14. In this configuration,switching is performed so that the electrode 12 is connected to theignition circuit 13 in ignition and the electrode 12 is connected to theflame detector 7 after detection of ignition.

[0094] In ignition, the switch 14 performs switching so that theelectrode 12 is connected to the ignition circuit 13, and ignition iscarried out as in the third embodiment. Meanwhile, when the ignitiontakes place and the flame is generated, the flame detector 7 detectsignition based on the temperature information of the combustion space 3which has been detected by the temperature detector 6. Upon detection,the switch 14 performs switching so that the electrode 12 is connectedto the flame detector 7. Thereby, the flame detector 7 detects the flamebased on an output current detected by the electrode 12 by theconventional flame detecting method as well as the flame detectingmethod using the temperature detector 6. Thus, the flame can be detectedby two methods using the temperature detector 6 and the electrode 12,and hence the flame can be detected more accurately.

[0095] Here, the flame condition in the upper region of the combustionspace 3 can be detected by the temperature detector 6, and the flamecondition in the lower region of the combustion space 3 can be detectedby the electrode 12 with tip end thereof placed in the lower regionwithin the combustion space 3 that is lower than the tip end of thetemperature detector 6. By detecting the flame conditions in pluralityof different regions within the combustion space 3, the abnormalcombustion condition can be detected as in the second embodiment.

[0096] First, in the case where combustion is performed normally, and aflame 11C is thereby generated, the flame detector 7 judges that theignition has occurred in the upper region of the combustion space 3,based on the temperature detected by the temperature detector 6 providedin the upper region of the combustion space 3 (vicinity of the exit ofthe combustion space 3). Concurrently with detection by the temperaturedetector 6, the output current from the electrode 12 placed in the lowerregion of the space 3 (in the vicinity of the fuel distributor 1) isdetected and the detected current value is converted into a voltagevalue. Based on whether or not the voltage value is larger than athreshold voltage, it is judged whether or not ignition has occurred. Inthis case, since the flame is formed in the lower region of thecombustion space 3, the output current becomes large, and hence, thevoltage is larger than the threshold voltage. So, the flame detector 7judges that the ignition has occurred in the lower region of thecombustion space 3. Thus, since it is judged that ignition has occurredin both of the upper and lower regions of the combustion space 3, normalcombustion is confirmed.

[0097] On the other hand, for example, if the combustion amount becomestoo large or the amount of air supply becomes small for some reasons,thereby causing the flame to be lifted to some degrees, abnormalcombustion takes place, and a flame 11B is generated in substantiallythe upper region of the combustion space 3. Such a flame 11B causes theupper region of the combustion space 3 to be heated greatly, therebyresulting in a temperature of this upper region higher than normal. Forthis reason, the temperature detected by the temperature detector 6provided in the upper region of the combustion space 3 becomes high.Based on this, the flame detector 7 judges that ignition has occurred inthe upper region of the combustion space 3. Conversely, the outputcurrent from the electrode 12 placed in the lower region of thecombustion space 3 is not detected because of absence of the flame inthe lower region of the combustion space 3, and therefore, the voltagevalue into which the current value has been converted becomes smallerthan the threshold voltage. From this, the flame detector 7 judges thatthe flame has vanished in the lower region of the combustion space 3.And, from these judgment as to ignition in the upper and the lowerregions of the combustion space 3, the abnormal combustion condition hasbeen confirmed.

[0098] Further, for example, the combustion amount becomes too small, orthe amount of air supply becomes large for some reasons, abnormalcombustion condition occurs, and a small flame 11A is generated in thelower region of the combustion space 3. When the flame 11A is generated,the output current from the electrode 12 is detected because of thepresence of the flame. In this case, the voltage value into which thedetected current value has been converted is larger than the thresholdvoltage, and based on this, the flame detector 7 judges that ignitionhas occurred in the lower region of the combustion space 3. On the otherhand, the temperature detected by the temperature detector 6 provided inthe upper region of the combustion space 3 becomes low because ofabsence of the flame. Based on this temperature information, the flamedetector 7 judges that the flame has vanished in the upper region of thecombustion space 3. From judgment of ignition in the upper and lowerregions of the combustion space 3, the abnormal combustion state isconfirmed.

[0099] In the first to fourth embodiments, the temperature detectingportion of the temperature detector is placed within the air injectionhole, but this is only illustrative. For example, a temperature detectormade of a heat-resistant material may extend further into the combustionspace. More specifically, the temperature detector may be placeddifferently from those in the first to fourth embodiments, so long as itis thermally insulated from a burner component around it and is exposedto an air flow injected from the air injection hole. It should be notedthat, if the tip end of the temperature detecting portion of thetemperature detector is set back to a considerable degree from theinterface between the air injection hole 9 and the combustion space 3,or is located between the outer wall and the inner wall of the airinjector, the temperature within the combustion space cannot be detectedaccurately, correctly, and smoothly. It is therefore necessary to placethe temperature detecting portion of the temperature detector at alocation to enable temperature variation in the combustion space to bedetected immediately, i.e., at least face the combustion space 3.

[0100] In the second to fourth embodiments, the tip end of thetemperature detecting portion side of the temperature detector is shapedto have a corner portion. Alternatively, as in the case of thealternative example of the first embodiment, the tip end of thetemperature detector may be hemispherical.

[0101] (Embodiment 5)

[0102]FIG. 8 is a view schematically showing a configuration of a fuelcell power generation system comprising a hydrogen generator includingthe burner of the present invention. As shown in FIG. 8, a fuel cellpower generation system 10 comprises a fuel cell 53 and a hydrogengenerator 52 as major components. The fuel cell 53 has the conventionalstructure.

[0103] The hydrogen generator 52 comprises a burner 50, a reformer 51,and a CO shifter 54. As the burner 50, the burner described in the firstto fourth embodiments is used. The reformer 51 and the CO shifter 54have the conventional structures. Within the reformer 51, CH₄ as thefuel gas is supplied, and a reforming reaction is conducted asrepresented by a reaction formula. Since the reforming reaction needs tobe carried out at a temperature as high as 650 to 700° C., in thehydrogen generator 52, the burner 50 heats the reformer 51. The reformedgas generated through the reforming reaction in the reformer 51 issupplied to the CO shifter 54. In the CO shifter 54, CO is removed fromthe reformed gas by the reaction represented by a reaction formula inFIG. 8. Thus, in the reformer 51 and the CO shifter 54, a hydrogen-richgas containing H₂ as a major component is generated, and is supplied tothe fuel cell 53 as the fuel gas. In the hydrogen generator 52, thehydrogen-rich gas (generated gas) containing large amount of CO isgenerated during start of the generator. However, such a generated gascannot be used in the fuel cell 53 because CO degrades the electrode ofthe fuel cell 53. For this reason, such a gas is supplied to the burner50 of the hydrogen generator 52 as the fuel gas. Although the generatedgas contains large amount of CO, the operation of the reformer 51 iscontrolled so that the conversion rate of CH₄ into H₂ and CO₂ in thereforming reaction becomes high, and therefore, the percentage ofunconverted hydrocarbon based combustible substance contained in thegenerated gas is low and the content of H₂ contained in the generatedgas is high.

[0104] The hydrogen-rich gas generated in the hydrogen generator 52 issupplied to the fuel cell 53, where reaction is conducted using thehydrogen-rich gas and oxygen contained in the air as represented by areaction formula in FIG. 7, thereby generating a power. An electricenergy derived from the fuel cell 53 is used for various purposes. Onthe other hand, the off-gas containing H₂ which remains unused after thereaction, which is included in the hydrogen-rich gas supplied to thefuel cell 53, is supplied to the burner 50 of the hydrogen generator 52and used as the fuel gas of the burner 50.

[0105] Hereinbelow, a flame detecting operation in the hydrogengenerator 52 in the fuel cell power generation system 100 (FIG. 8)including the burner 50 of the fourth embodiment in FIG. 7 will bedescribed with reference to FIG. 9.

[0106]FIG. 9 is a view showing operation data of the hydrogen generator52 in the fuel cell power generation system 100 of this embodiment. Asshown in FIG. 9, a graph A represents time-series variation intemperature of the reformer 51 of the hydrogen generator 52, graph Brepresents time-series variation in temperature of the combustion space3 detected by the temperature detector 6, and graph C representstime-series variation in the voltage value into which the output currentvalue from the electrode 12 (FIG. 7) has been converted.

[0107] As shown in the graph A, when the fuel cell power generationsystem 100 starts and the burner 50 is ignited, the temperature of thereformer 51 increases after a lapse of a predetermined time afterignition because of its large heat capacity. And, after a lapse ofseveral minutes, the temperature of the reformer 51 increases to apredetermined value (about 650 to 700° C.) and is kept at thistemperature.

[0108] On the other hand, as shown in the graph B, when the burner 50 isignited, temperature variation within the combustion space 3 can bedetected by the temperature detector 6, and the detected temperaturegradually increases just after the voltage value of the electrode 12increases as described later. Then, after a lapse of time, and apredetermined temperature is reached, the detected temperature becomesconstant.

[0109] As shown in the graph C, since the generated gas containing ahigh content of hydrocarbon based combustible substance (or off-gas) issupplied to the burner 50 during ignition, the voltage value into whichthe output current value from the electrode 12 has been convertedincreases in a moment of time. As described above, this voltage value isaffected by a composition of the generated gas, and hence varies asdescribed below with a lapse of an operation time. Until the reformer 51reaches the predetermined temperature, a conversion rate in thereforming reaction gradually increases, and the concentration ofhydrogen contained in the generated gas which is obtained from thereformer 51 gradually increases. Correspondingly, the content of thehydrocarbon based combustible substance contained in the generated gasgradually decreases. As a result, the voltage value of the electrode 12decreases regardless of the increase in the temperature of the reformer51. And, when the reformer 51 is kept at the predetermined temperature,the voltage value becomes constant at a lower limit value. In this case,if the conversion rate in the reformer 51 is increased in order togenerate a large amount of hydrogen in the hydrogen generator 52, thevoltage value is further reduced.

[0110] As should be appreciated from the above, in the hydrogengenerator 52, the flame can be detected by the conventional flamedetecting method based on the voltage value of the electrode 12 duringignition and a predetermined period thereafter. In particular, duringignition, because of high responsivity to ignition, the flame can bedetected more accurately than detection by the temperature detector 6.However, when the temperature of the reformer 51 increases, therebycausing the conversion rate in the reforming reaction to increase,detection using the electrode 12 becomes difficult under the influenceof noises. Accordingly, the flame is detected using the electrode 12 inignition, and thereafter, under the condition in which the gascontaining low content of hydrocarbon based combustible substancebecause the conversion rate in the reformer 51 is high, is supplied tothe burner 50, the flame is detected using the temperature detector 6.Thereby, generation of the flame can be detected as soon as ignitiontakes place, and then, the flame condition can be detected accuratelyunder the condition in which combustion is performed in the burner 50using the gas containing low content of hydrocarbon based combustiblesubstance as the fuel gas.

[0111] In accordance with the above configuration, during operation ofthe fuel cell power generation system 100, the flame can be detectedaccurately in the hydrogen generator 52 regardless of the composition ofthe fuel gas supplied to the burner 50. Therefore, combustion is carriedout by the burner 50 using the off-gas or the generated gas as the fuelgas. As a result, it is possible to achieve a power generation systemusing the off-gas or the generated gas as the fuel, in which powergeneration efficiency is high, burden on environment is small, andsafety is high.

[0112] While the burner of the present invention is used for heating thehydrogen generator in the fuel power generation system, this may be usedas a burner using the gas containing a low content of combustiblesubstances including compound at least containing carbon and hydrogen asthe fuel gas, for example, a burner for heating a hot water supplydevice.

[0113] Numerous modifications and alternative embodiments of theinvention will be apparent to those skilled in the art in the light ofthe foregoing description. Accordingly, the description is to beconstrued as illustrative only, and is provided for the purpose ofteaching those skilled in the art the best mode of carrying out theinvention. The details of the structure and/or function may be variedsubstantially without departing from the spirit of the invention.

What is claimed is:
 1. A burner having a fuel distributor configured toinject a fuel supplied from a fuel supply device; and an air injectorplaced such that the air injector surrounds the fuel distributor so asto form a combustion space around the fuel distributor and having an airinjection hole through which air supplied from an air supply device isinjected, the air injected from the air injection hole and the fuelinjected from the fuel distributor being combusted to allow a flame tobe generated in the combustion space, the burner comprising: atemperature detector for detecting a temperature of the combustionspace, the temperature detector having a temperature detecting portionlocated within the air injection hole or in an air flow passage of thecombustion space; and a flame detector for detecting a condition of theflame within the combustion space, based on the temperature detected bythe temperature detector.
 2. The burner according to claim 1, whereinthe temperature detector is placed such that the temperature detectingportion is located within the air injection hole or within thecombustion space in the vicinity of the air injection hole.
 3. Theburner according to claim 1, wherein the temperature detector is placedso as to penetrate the air injector.
 4. The burner according to claim 1,wherein the temperature detecting portion of the temperature detector isthermally insulated from an inner face of the air injection hole.
 5. Theburner according to claim 4, wherein a gap is formed between thetemperature detector and the inner face of the air injection hole, and awidth of the gap is substantially uniform over an outer periphery of thetemperature detector.
 6. The burner according to claim 4, wherein theair injector has a plurality of air injection holes, and across-sectional area of the gap between the air injection hole withinwhich the temperature detector is provided and the temperature detectoris substantially equal to a cross-sectional area of the air injectionhole within which the temperature detector is not provided.
 7. Theburner according to claim 1, wherein the temperature detector has thetemperature detecting portion at an end portion thereof, and a body ofthe temperature detector is contained within the air injector.
 8. Theburner according to claim 7, wherein an end portion of the temperaturedetecting portion side of the temperature detector is substantiallycovered with an oxidation film.
 9. The burner according to claim 7,wherein an end portion of the temperature detecting portion side of thetemperature detector is substantially hemispherical.
 10. The burneraccording to claim 1, wherein the temperature detector is asheath-shaped thermo couple.
 11. The burner according to claim 1,wherein a plurality of temperature detectors are provided at differentpositions within the combustion space to detect temperatures ofdifferent regions within the combustion space.
 12. The burner accordingto claim 1, wherein the combustion space has a cross-sectional area thatincreases toward a flame radiation direction.
 13. The burner accordingto claim 1, further comprising: an electrode contained within the fueldistributor and having an end portion that protrudes into the combustionspace; and an ignition circuit electrically connected to the electrode,for applying a voltage to the electrode to allow electric discharge fromthe electrode to occur within the combustion space.
 14. The burneraccording to claim 13, further comprising: a switch configured toperform switching so that the electrode is connected to the ignitioncircuit during ignition, and the electrode is connected to the flamedetector when the flame detector judges that ignition has occurred basedon temperature information of the combustion space from the temperaturedetector, wherein the flame detector detects the flame based on thetemperature information from the temperature detector and detects theflame based on an output current from the electrode.
 15. The burneraccording to claim 14, wherein the end portion of the electrode thatprotrudes into the combustion space is placed in a region different froma region of the combustion space in which the temperature detector isplaced, to detect the flame in the region which is different from theregion where the flame is detected by the temperature detector.
 16. Theburner according to claim 15, wherein the temperature detector detectsthe flame in an upper region of the combustion space in the flameradiation direction, and the electrode detects the flame in a lowerregion of the combustion space in the flame radiation direction.
 17. Ahydrogen generator comprising: a burner having a fuel distributorconfigured to inject a fuel supplied from a fuel supply device; and anair injector placed such that the air injector surrounds the fueldistributor so as to contain the fuel distributor and form a combustionspace around the fuel distributor and having an air injection holethrough which air supplied from an air supply device is injected, theair injected from the air injection hole and the fuel injected from thefuel distributor being combusted to allow a flame to be generated in thecombustion space, the burner including: a temperature detector fordetecting a temperature of the combustion space, the temperaturedetector having a temperature detecting portion located within the airinjection hole or in an air flow passage of the combustion space; and aflame detector for detecting a condition of the flame within thecombustion space, based on the temperature detected by the temperaturedetector, and a reformer for generating a reformed gas containinghydrogen by a reforming reaction of a feed material including a compoundcontaining at least carbon and hydrogen, the burner being configured toheat the reformer.
 18. A fuel cell power generation system comprising: ahydrogen generator including: a burner having a fuel distributorconfigured to inject a fuel supplied from a fuel supply device; and anair injector placed such that the air injector surrounds the fueldistributor so as to contain the fuel distributor and form a combustionspace around the fuel distributor and having an air injection holethrough which air supplied from an air supply device is injected, theair injected from the air injection hole and the fuel injected from thefuel distributor being combusted to allow a flame to be generated in thecombustion space, the burner including: a temperature detector fordetecting a temperature of the combustion space, the temperaturedetector having a temperature detecting portion located within the airinjection hole or in an air flow passage of the combustion space; and aflame detector for detecting a condition of the flame within thecombustion space, based on the temperature detected by the temperaturedetector, and a reformer for generating a reformed gas containinghydrogen by a reforming reaction of a feed material including a compoundcontaining at least carbon and hydrogen, the burner being configured toheat the reformer; and a fuel cell configured to generate a power usinga gas containing hydrogen as a major component which is supplied fromthe hydrogen generator to a fuel electrode and an oxidizing gas suppliedto an oxidizing electrode.